Air France - radar detection

[thebullettrain]

I do not think this question has been asked before. Why wasn't this plane under Brazilian or Western African radar when it had its problems?

[Mattt]

Big thread elsewhere.

[eharding]

thebullettrain said:

I do not think this question has been asked before. Why wasn't this plane under Brazilian or Western African radar when it had its problems?

Same reason it wasn't under Farnborough Radar......

[sirtyro]

It was flying through a non-radar zone where pilots just depend upon radio....I didnt think they existed either but think it was on the BBC article about it

[RDE]

Every time an aircraft crosses the Atlantic, it leaves radar cover and will usually be controlled using a procedural service that relies on position reports from the aircraft at various reporting points.

The report from the airline would probably have said something like the aircraft "left Brazilian radar at time XX", which was immediately garbled by numpty journalists to mean that the blip just disappeared from the screen unexpectedly.

Even in the relatively small area of the UK, you could be outside a workable radar area, as air traffic units will have limitations on what range they can provide a service to, even if a return is visible. It's also worth mentioning that the base of radar cover gets higher as you move out from the radar head - roughly 1000ft for every ten miles. So if you're 30 miles from the unit at 2000ft, you might not be seen.

Edited by RDE on Friday 5th June 23:21

[dnb]

Simple - there aren't that many radars floating around on the sea, and their range is limited in a lot of ways.

An example: Say the aircraft is flying at 10,000m (30kft) altitude and the radar antenna is at a height of 40m above sea level, the radar will have line-of-sight on the aircraft up to a range of about 440km (237n.mi). Unless the radar is particularly powerful, it won't actually be able to reliably detect the aircraft until it is at a considerably lesser range.
The diameter of the earth is 12,756 km, so you'd need a lot of radars to get complete coverage.

There are other technologies for tracking airliners such as "Mode S" transponders, where the aircraft broadcast their positions when interrogated by IFF antennae. You can passively intercept this with the right equipment. Again, it's not much use over the sea if no-one is around to interrogate the aircraft.

[Eric Mc]

It jus shows how unknowledgeable people are if they think that 100% of the globe is covered by air traffic control radar.

[Muncher]

Why aren't they tracked by GPS? i.e. their GPS verified position is relayed back to air traffic control using radiowaves?

[thebullettrain]

Eric Mc said:

It jus shows how unknowledgeable people are if they think that 100% of the globe is covered by air traffic control radar.

That is unfair - I do find it very strange that flights over the Atlantic are not tracked by some means or another. Given all the technology we have it's not very hard - what about some GPS variant?

[scorp]

thebullettrain said:

Eric Mc said:

It jus shows how unknowledgeable people are if they think that 100% of the globe is covered by air traffic control radar.

That is unfair - I do find it very strange that flights over the Atlantic are not tracked by some means or another. Given all the technology we have it's not very hard - what about some GPS variant?

GPS works by receiving signals from satellites, not transmitting to them, so there is no way to send information back via that network. You would probably need a internationally run gps-like network of satellites to cover the whole earth which supports relaying realtime data from lots of aircraft, which i imagine isn't too cheap. Saying that, what's the coverage for satellite phones ? maybe a system could be made using that..

Edited by scorp on Saturday 6th June 06:17

[SleeperCell]

The technology for 2 way GPS tracking of airliner is available, but not mandatory or standardised so there are different systems and not that many operators can be bothered with the cost if it's not required. I think it's mainly freight companies and private jets that employ such systems, though there are the odd airline such as Lifthansa, but only because they want to demo their own developed system. I believe there are plans being drawn up for a standard system of GPS tracking for all aircraft but it's not due to be finalised until 2010 and airlines wont need to comply until 2020.

[Eric Mc]

thebullettrain said:

Eric Mc said:

It jus shows how unknowledgeable people are if they think that 100% of the globe is covered by air traffic control radar.

That is unfair - I do find it very strange that flights over the Atlantic are not tracked by some means or another. Given all the technology we have it's not very hard - what about some GPS variant?

Radar works by a s radar transmitter bouncing a radio signal off the target object. The radio transmissions are usually VHF, UHF or Microwave which travel in straight lines. Therefore, they do not curve around the earth's horizon. Once an aircraft is far enough away from the radar station, the radar signal will not pick it up as the aircraft dips below the horozon.
The higher the aircraft is flying, the longer it will remain visible to the radar system.

Once aircraft start crossing large oceans, they pretty soon leave the tracking stations behind and move out of radar range.

The only way they could be continually tracked on radar would be to have floating radar stations placed at strategic locations in the world's oceans.

GPS tracking is still fairly recent technology - compared to radar - and it will take decades for all the worlds airliners to be fitted out with this type of equipment. However, GPS is of more use to the crew to allow them to know where they are rather than for ground controllers to track the aircraft.

[thebullettrain]

Thanks for the explanation.